1. Field of the Invention
The present invention relates to a heat-insulated port liner arrangement which is used to prevent a decrease in temperature of an exhaust gas in an internal combustion engine.
2. Description of the Related Art
Japanese Utility Model Application (OPI) No. 82455/83 discloses an arrangement for preventing the temperature of exhaust gas from decreasing in an internal combustion engine. Such an arrangement uses a cylinder head with exhaust ports made of ceramics. This facilitates the cleaning of the exhaust ports and provides them with improved heat insulation properties.
The exhaust port of a cylinder head for an internal combustion engine is formed by producing a ceramic port liner, covering it with ceramic fibers, and then casting the cylinder head body from molten metal around the port liner assembly. In casting the cylinder head around the port liner arrangement, the heat insulation properties of the port liner arrangement cause cooling of the molten metal to be retarded in the area around the port liner arrangement. This retarded cooling causes blowholes to form in the neighborhood of the port liner arrangement. Such blowholes decrease sealability and allow leakage of gases from the combustion chamber and leakage of cooling water from the cooling system. It also has been found that poor wetting properties of the refractory fibers in their interface with the casting metal is also responsible for the formation of blowholes.
It is an object of the present invention to provide a heat insulated port liner arrangement which, when casting a cylinder head around the port liner arrangement, does not cause cooling of the molten metal to be substantially retarded in the area around the port liner arrangement.
It is another object of the present invention to provide a heat insulated port liner arrangement which does not cause blowholes to form in the neighborhood of the port liner arrangement when a cylinder head is cast around the port liner arrangement.
It is still a further object of the present invention to provide a heat insulated port liner arrangement in which sealability is not decreased and leakage of gases from the combustion chamber and leakage of cooling water from the cooling system does not occur.
It is still an additional object of the present invention to provide a heat insulated port liner arrangement having good wetting properties on its interface with the metal of the cylinder head.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.